THURSDAY, Sept. 5 (HealthDay News) -- Cognitive behavioral therapy can be a powerful tool for preventing depression, equaling or exceeding the effectiveness of antidepressants and other types of care, according to two new studies.

Follow-up cognitive therapy can be as effective as antidepressant medications in preventing a relapse for patients at high risk for another bout of depression, researchers reported in the first study, which was published online Sept. 4 in the journal JAMA Psychiatry.

Adults coming out of acute depression are less likely to suffer a relapse if they receive an additional eight months of either cognitive therapy or the antidepressant Prozac (fluoxetine) after finishing an initial round of cognitive therapy, the report concluded.

"Everybody did better than they would have if they hadn't had treatment," said study author Robin Jarrett, the Elizabeth H. Penn Professor of Clinical Psychology at the University of Texas Southwestern Medical Center in Dallas. "If you treat a patient with cognitive therapy and they do well, then the patient would have a choice: You could treat them with either fluoxetine or therapy."

In the second study, also published online Sept. 4 in JAMA Psychiatry, researchers from Boston Children's Hospital found that cognitive behavioral therapy did better than usual forms of care in preventing depression in at-risk teens.

Teens who received cognitive-behavioral therapy were significantly less likely to suffer a depressive episode than those who were referred to therapists for usual care, which typically involves either standard therapy or medication, said Dr. William Beardslee, director of Baer Prevention Initiatives at the hospital and the Gardner/Monks Professor of Child Psychiatry at Harvard Medical School.

"People at risk for depression often have a very gloomy sense of the future and will misinterpret communications: I'm being rejected or those people don't like me or what I do makes no difference," Beardslee said. "What one tries to do is show that actions do make a difference, and do that in a gentle, supportive way."

The first study involved 241 adults who had responded well to cognitive therapy but were at high risk of relapse for depression. They received treatment at the University of Texas Southwestern Medical Center and the University of Pittsburgh Medical Center.

Researchers broke the group roughly into thirds. The first two thirds received eight months of continuing treatment, either through additional cognitive therapy or by taking Prozac. The final third received a placebo pill.

The people who received continuing treatment had relapse rates that were half that of the placebo group -- about 18 percent for either cognitive therapy or fluoxetine, compared with 33 percent for placebo pills.

The protective effect, however, wore off after treatment ended. Two and a half years later, all three groups had similar relapse rates, although rates in the placebo group still tended to be slightly higher.

Dr. Sudeepta Varma, a clinical assistant professor of psychiatry at the NYU Langone Medical Center in New York City, said there is a higher likelihood of depression reoccurring with each episode of depression.

"For example, with individuals who have had three or more episodes, there is a 95 percent chance of reoccurrence," Varma said.

"I hate to break the bad news when my patients ask about this, but I tell them that there are some people who fall in this category who are going to need treatment indefinitely given their prior history of multiple depressive episodes and perhaps previous incomplete remission histories," she said.

The second study involved 316 teenagers who were at risk for depression because either their parents suffered from depression or they themselves showed symptoms or had prior instances.

The teens received cognitive-behavioral group therapy in eight weekly 90-minute group sessions followed by six monthly continuation sessions at sites in Boston, Nashville, Pittsburgh and Portland, Ore.

"We try to get kids to think of a range of options," Beardslee said. "State what the problem is -- let's say they can't get over a relationship and they feel persistently sad -- then try to get them to the goal by brainstorming all the possible solutions and trying some."

During a 33-month follow-up period, the kids who received the therapy had significantly fewer depressive episodes than those who were referred for usual psychiatric care.

"We wanted to see if this intervention could be delivered systematically and reliably in four different sites in the U.S., and the answer is yes," Beardslee said. "It's a step on the way to eventually disseminating the intervention widely."

There was one drawback. Kids who underwent cognitive behavioral therapy at the same time their parents were suffering depression received no benefit.

"This speaks to the fact that the parental depression must also be simultaneously addressed, and I imagine both individually but also in the family context through family therapy," Varma said. "This study says that [cognitive behavioral therapy] prevention is highly effective, but we need to look at the big picture. And this makes sense. Depression for young people does not exist in a bubble, and if we can support the family we can help the adolescent."